The U.S. Pat. No. 4,483,125 discloses such an apparatus which conveys a number of trays each containing food on a belt-driven conveyer aligned in file at equal intervals. Concurrently, the apparatus sequentially converts a belt-like film into tubular form in the periphery of each tray while continuously drawing out the film in the longitudinal direction. Next, the apparatus causes a cutting unit to cut off the tubular film between a pair of trays passing over the cutting unit. At the same time, the apparatus causes a pair of suction tubes aligned in the front and on the back apart from the cutting unit to pull both edges of the cut-off film in the direction of the ground surface. Next, the apparatus folds both edges of the film in the front of the forward-moving tray while causing those suction tubes to respectively hold both edges of the film and then fold both edges alongside of the bottom surface of the tray by applying the forward movement of the tray, whereas both edges of the film behind the forwarding tray are also folded along-side of the bottom surface of the tray in the manner of being caught by a pair of rods which shift themselves at a speed faster than that of the moving tray while holding both edges by means of the suction tubes.
On the other hand, the apparatus disclosed in the above U.S. Pat. No. 4,483,125 generates the following problem while folding both edges of the film behind the forward-moving tray.
Concretely, a pair of rods which are secured to a pair of endless chains and available for catching both edges of the film behind the tray shift themselves at a speed faster than that is used for conveying trays via the rotation of those endless chains. In consequence, these rods shifting themselves at a fast speed respectively cause both edges of the film behind the tray to instantaneously leave the suction tubes, and as a result, the film cannot be elongated to full extent.
In addition, generally, the bottom surface of each tray has a lateral width which is narrower than that of the top surface. In particular, the less the volume of the tray, the wider the lateral width of a tubular film than the width of the bottom surface of the tray. This in turn incurs unwanted protrusion of the folded film from the lateral width of the tray.